Optical beam splitter for use in an optoelectronic module, and a method for performing optical beam splitting in an optoelectronic module

ABSTRACT

An apparatus and a method are provided for mechanically coupling an optics system holder of an optoelectronic module with an optical connector of the optoelectronic module. The apparatus comprises first and second retention features formed on opposite ends of the optics system holder and first and second latches formed on opposite ends of the optical connector. When a lower surface of the optical connector is pressed against an upper surface of the optics system holder, the first and second retention features engage the first and second latches, respectively, such that the first and second latches flex to a limited degree and exert a spring force on the optical connector that firmly presses the lower surface of the optical connector against the upper surface of the optics system holder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.12/828,278, filed on Jun. 30, 2010, entitled “AN OPTICAL BEAM SPLITTERFOR USE IN AN OPTOELECTRONIC MODULE, AND A METHOD FOR PERFORMING OPTICALBEAM SPLITTING IN AN OPTOELECTRONIC MODULE.” The Applicants hereby claimthe benefit of the filing date of application Ser. No. 12/828,278 andhereby incorporate it by reference herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

The invention relates to optoelectronic modules. More particularly, theinvention relates to an optical beam splitter for use in anoptoelectronic module for splitting a beam into at least two portionsthat have different levels of optical power.

BACKGROUND OF THE INVENTION

In optical communications networks, optoelectronic modules are used totransmit and/or receive optical signals over optical fibers. Theoptoelectronic module may be configured as an optical transmitter thattransmits optical signals, an optical receiver that receives opticalsignals, or an optical transceiver that transmits and receives opticalsignals. On the transmit side of an optical transmitter or transceivermodule, a light source (e.g., a laser diode) generates amplitudemodulated optical signals that represent data, which are opticallycoupled by an optics system of the module into an end of a transmitoptical fiber. The signals are then transmitted over the transmit fiberto a receiver node of the network. On the receive side of an opticalreceiver or transceiver module, an optics system of the module receivesoptical signals output from an end of a receive optical fiber andfocuses the optical signals onto an optical detector (e.g., aphotodiode), which converts the optical energy into electrical energy.

In some laser-based optoelectronic modules, a portion of the light thatis produced by the laser is used to monitor the optical output powerlevel of the laser and to adjust the optical output power level of thelaser as needed. Typically, it is desirable to maintain the opticaloutput power level of the laser at a substantially constant,predetermined level during operations. To accomplish this, manyoptoelectronic modules include components that together make up afeedback control system for monitoring the average optical output powerlevel of the laser and adjusting the bias and/or modulation currents ofthe laser as needed to maintain that average optical output power levelat a substantially constant, predetermined level. The feedback pathcomponents typically include a beam splitter, a monitor photodiode,analog-to-digital (ADC) circuitry, and controller circuitry. The beamsplitter causes a portion of the beam that is produced by the laser tobe split off and directed onto a monitor photodiode. The monitorphotodiode produces an analog electrical signal in response to the lightthat is directed onto it by the beam splitter. The analog electricalsignal is converted into a digital electrical signal by the ADCcircuitry. The controller circuitry processes the digital electricalsignal and causes the laser modulation and/or bias currents to beadjusted accordingly.

Beam splitters are manufactured in a variety of configurations andtypically comprise one or more reflective, refractive and/or diffractiveelements. In a typical beam splitter configuration, a first portion ofthe main beam produced by the laser passes through the beam splitterwith very little if any of the light being reflected, refracted ordiffracted. This portion of the main beam is then coupled into the endof the transmit optical fiber for transmission over the transmit opticalfiber. At the same time, a second portion of the main beam is reflected,refracted and/or diffracted by the beam splitter to cause the secondportion to be directed onto the monitor photodiode.

Usually, the first and second portions each contain about 50% of theoptical power that was contained in the main beam. This symmetric, oreven, split of the optical power can cause problems in some cases.Typical lasers that are used in optoelectronic modules produce lighthaving optical power levels that are much greater than safety limits forthe human eye. Even at 50% of the optical power of the main beam, thefirst portion of the light will have an optical power level that isgreater than eye safety limits. It is generally not possible, or atleast very difficult, to run a laser at the high speed required for theoptical communications link and simultaneously reduce the optical outputpower level of the laser to a level that is within eye safety limits.For this reason, steps are often taken to ensure that the light that isto be transmitted over the transmit optical fiber is attenuated to anoptical power level that is within the safety limits.

Accordingly, a need exists for an optical beam splitter for use in anoptoelectronic module that is capable of providing an uneven, orasymmetrical, split of the main beam produced by the laser such that theportion of the light that is split off and coupled into the end of thetransmit optical fiber as the optical data signal has an optical powerlevel that is within human eye safety limits and yet that has sufficientoptical power to avoid signal degradation problems.

SUMMARY OF THE INVENTION

The invention is directed to an apparatus and a method for mechanicallycoupling an optics system holder of an optoelectronic module with anoptical connector of the optoelectronic module. The apparatus comprisesfirst and second retention features formed on opposite ends of theoptics system holder and first and second latches formed on oppositeends of the optical connector. When a lower surface of the opticalconnector is pressed against an upper surface of the optics systemholder, the first and second retention features engage the first andsecond latches, respectively, such that the first and second latchesflex to a limited degree and exert a spring force on the opticalconnector that firmly presses the lower surface of the optical connectoragainst the upper surface of the optics system holder.

The method comprises providing an optics system holder that holds anoptics system and which has first and second retention features formedon opposite ends thereof, providing an optical connector having firstand second latches formed on opposite ends thereof, and pressing a lowersurface of the optical connector against an upper surface of the opticssystem holder to cause the first and second retention features to engagethe first and second latches, respectively. When the first and secondretention features engage the first and second latches, respectively,the first and second latches flex to a limited degree and exert a springforce on the optical connector that firmly presses the lower surface ofthe optical connector against the upper surface of the optics systemholder.

These and other features and advantages of the invention will becomeapparent from the following description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an illustrative embodiment of a bidirectional opticallink comprising an optical fiber and optoelectronic modules coupled toopposite ends of an optical fiber that incorporate optical beamsplitters in accordance with an illustrative embodiment of theinvention.

FIG. 2 illustrates a side cross-sectional view of an illustrativeembodiment of one of the optical beam splitters illustrated in FIG. 1.

FIGS. 3A and 3B illustrate bottom and top perspective views,respectively, of a glass wafer having arrays of the optical elements ofthe optical beam splitter shown in FIG. 2 formed on the bottom and topsurfaces thereof.

FIGS. 4A and 4B illustrate the bottom and top surfaces of the wafershown in FIGS. 3A and 3B after an epoxy replication process has beenused to form the refractive optical elements on the bottom surface ofthe wafer and to form the optical coupling structure on the top surfaceof the wafer.

FIGS. 5A and 5B illustrate bottom and top perspective views,respectively, of the optical beam splitter shown in FIG. 2.

FIG. 6 illustrates a top perspective view of an optical transceivermodule having an optical beam splitter holder coupled therewith thatholds the optical beam splitter shown in FIG. 2.

FIG. 7 illustrates a cross-sectional perspective view of the opticalbeam splitter holder shown in FIG. 6 with the optical beam splitter heldtherein.

FIG. 8 illustrates a perspective view of the optical transceiver moduleshown in FIG. 6 having an optical connector coupled to it, which, inturn, has the lens assembly shown in FIG. 2 coupled to it.

FIGS. 9A and 9B illustrate top and bottom perspective views,respectively, of the optical connector shown in FIG. 8 having the lensassembly shown in FIG. 2 coupled to it.

FIG. 10 illustrates a cross-sectional side view of the opticaltransceiver module shown in FIG. 8 coupled with the optical connectorshown in FIGS. 9A and 9B, which, in turn, is coupled with the lensassembly.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

The invention is directed to an apparatus and a method for mechanicallycoupling an optics system holder of an optoelectronic module with anoptical connector of the optoelectronic module. The apparatus comprisesfirst and second retention features formed on opposite ends of theoptics system holder and first and second latches formed on oppositeends of the optical connector. When a lower surface of the opticalconnector is pressed against an upper surface of the optics systemholder, the first and second retention features engage the first andsecond latches, respectively, such that the first and second latchesflex to a limited degree and exert a spring force on the opticalconnector that firmly presses the lower surface of the optical connectoragainst the upper surface of the optics system holder.

In accordance with an illustrative, or exemplary, embodiment, the opticssystem that is held by the optics system holder is an optical beamsplitter. Therefore, examples of the optical beam splitter, of anoptoelectronic module that incorporates the optical beam splitter, andof a link that incorporates the optoelectronic module will first bedescribed. Then, the apparatus and method for mechanically coupling theholder of the optoelectronic module with the optical connector of theoptoelectronic module will be described.

The optical beam splitter is configured to split a main beam produced bya laser into at least first and second light portions that havedifferent optical power levels. The first light portion, which is to becoupled into an end of a transmit optical fiber of an opticalcommunications link, has an optical power level that is within eyesafety limits and yet has sufficient optical power to avoid signaldegradation problems. The first light portion has an optical power levelthat is less than the optical power level of the second light portion.The optoelectronic module in which the optical beam splitter is employedmay be an optical transmitter module or an optical transceiver module.The optical communications link may be a unidirectional optical link ora bidirectional optical link. However, in order to demonstrate thevarious capabilities and advantages of the optical beam splitter, abidirectional configuration of the optical beam splitter that enables itto be used in a bidirectional optical link will be now described withreference to the figures.

FIG. 1 depicts an illustrative embodiment of a bidirectional opticallink 1 comprising an optical fiber 10 and optoelectronic modules 20 and30 coupled to opposite ends of an optical fiber 10, each of whichincorporates an optical beam splitter in accordance with an illustrativeembodiment of the invention. In accordance with this illustrativeembodiment, the optoelectronic modules 20 and 30 are optical transceivermodules. The optical transceiver module 20 coupled to end 10 a of theoptical fiber 10 includes a TX 20 a, an RX 20 b, and an optical couplingsystem 50. The optical coupling system 50 of the optical transceivermodule 20 incorporates an optical beam splitter 50 a and one or morerefractive, reflective and/or diffractive optical elements (not shown),as will be described below in detail with reference to FIG. 2. Theoptical beam splitter 50 a and the other optical elements (not shown)may be separate elements or they may be integrated into a singleintegrated optical device, as will be described below with reference toFIG. 2. The optical transceiver module 30 coupled to end 10 b of theoptical fiber 10 includes a TX 30 a, an RX 30 b, and an optical couplingsystem 60 Like the optical coupling system 50, the optical couplingsystem 60 incorporates an optical beam splitter 60 a and one or morerefractive, reflective and/or diffractive optical elements. The opticaltransceiver module 20 includes a beam stop 70 a and a monitor photodiode70 b. Likewise, the optical transceiver module 30 includes a beam stop80 a and a monitor photodiode 80 b.

As will be described below in more detail with reference to FIG. 2, theTXs 20 a and 30 a of the optical transceiver modules 20 and 30 eachinclude at least one light source, which is typically a laser diode,such as a vertical cavity surface emitting laser diode (VCSEL), forexample, and light source driver circuitry. The RXs 20 b and 30 b of theoptical transceiver modules 20 and 30 each include at least oneoptical-to-electrical (OE) conversion device, such as a photodiode, andreceiver circuitry. The optical fiber 10 is typically a multi-mode (MM)optical fiber, such as, for example, an OM3 MM optical fiber. Inaccordance with this illustrative embodiment, the TXs 20 a and 30 a andthe RXs 20 b and 30 b all operate at the same wavelength. The opticalcoupling systems 50 and 60 allow the optical transceiver modules 20 and30 to simultaneously transmit and receive optical data signals that areat the same wavelength, which may be, for example, 850 nanometers (nm),1310 nm or 1550 nm. The invention, however, is not limited with respectto the wavelength that is used for this purpose.

The optical transceiver modules 20 and 30 operate as follows. In thetransmit direction of the optical transceiver module 20, the TX 20 aproduces a main beam of laser light having wavelength λ1, which isreceived by the optical coupling system 50. The optical coupling system50 collimates the main beam, splits the main beam into at least firstand second light portions L1 and L2, and tilts at least the first lightportion L1 at a preselected angle relative to the angle of incidence ofthe main beam on the optical coupling system 50. In FIG. 1, the tiltingof the first light portion L1 is not shown for ease of illustration. Anexample of an actual physical implementation of the optical couplingsystem 50 is described below in detail with reference to FIG. 2.

With reference again to FIG. 1, the first light portion L1 has lessoptical power than the second light portion L2. The first light portionL1 has between about 10% and 30% of the optical power of the main beam,and typically has about 20% of the optical power of the main beam. Thesecond light portion L2 has between about 70% and 90% of the opticalpower of the main beam, and typically has about 80% of the optical powerof the main beam. As will be described below in more detail withreference to FIG. 2, most of the second light portion L2 is absorbed bythe beam stop 70 a and a very small amount of the second light portionL2 is received by the monitor photodiode 70 b and used as opticalfeedback to control optical output power level of the laser diode.Although the beam stops/monitor photodiodes 70 a/70 b and 80 a/80 b aredepicted in FIG. 1 as being collocated, this is merely for ease ofillustration, as will become clear from the description below of FIG. 2.

The first light portion L1 passes through the beam splitter 50 a and isbrought to a focal point by the optical coupling system 50 at the end 10a of the MM optical fiber 10. The first light portion L1 corresponds tothe first optical data signal, which is then transmitted along the MMoptical fiber 10 to the optical transceiver 30 coupled to the oppositeend 10 b of the MM optical fiber 10. As indicated above, most of thesecond light portion L2 is directed by the optical coupling system 50onto the beam stop 70 a while a very small portion of the second lightportion L2 is directed onto the monitor photodiode 70 b. Typically, thebeam stop 70 a receives and absorbs about 80% of the optical power ofthe main beam. By absorbing the light received thereby, the beam stop 70a prevents near-end stray light from affecting the performance of theoptical transceiver module 20. As indicated above, the monitorphotodiode 70 b is used in a power monitoring feedback loop to monitorthe optical output power of the laser diode of the TX 20 a. The monitorphotodiode 70 b typically receives only about 1% to 2% of the opticalpower of the main beam.

Transparent stubs 90 a and 90 b are placed on the ends 10 a and 10 b,respectively, of the MM optical fiber 10. The stubs 90 a and 90 b havefirst ends that attach to respective optical ports 105 and 115,respectively, of the optical transceiver modules 20 and 30,respectively. The stubs 90 a and 90 b have second ends that attach tothe ends 10 a and 10 b, respectively, of the MM optical fiber 10. Theends of the stubs 90 a and 90 b that attach to the optical ports 105 and115 have anti-reflection coatings thereon. The ends of the stubs 90 aand 90 b that have the anti-reflection coatings thereon will be referredto hereinafter as the entrance facets of the stubs 90 a and 90 b. Theends of the stubs 90 a and 90 b that attach to the ends 10 a and 10 b ofthe MM optical fiber 10 are attached in such a way that no light isreflected at the interfaces of the stubs 90 a and 90 b and the ends 10 aand 10 b, respectively, of the MM optical fiber 10. The stubs 90 a and90 b essentially eliminate all interface reflections at the opticalports 105 and 115, thereby preventing signal degradation due tocross-talk that might otherwise be caused by reflections of light atthese interfaces. It should also be understood that as part of normaloperation of the optical transceiver modules 20 and 30, the fiber 10 maybe attached to and detached from the respective optical ports 105 and115, and hence to and from the respective stubs 90 a and 90 b. Stubs ofthe type that may be used for this purpose are well known in the art.Therefore, persons of ordinary skill in the art will understand, in viewof the description provided herein, the manner in which the stubs 90 aand 90 b may be designed and implemented in the bi-directional opticallink 1 shown in FIG. 1.

In the receive direction of the optical transceiver module 20, anoptical data signal of wavelength λ1 that has been transmitted by theoptical transceiver module 30 over the MM optical fiber 10 is receivedby the optical coupling system 50. The stub 90 b prevents interfacereflections from occurring in the optical transceiver module 30 thatmight otherwise result in cross-talk and signal degradation. The beamsplitter 50 a reflects the received optical data signal in a directiontoward the RX 20 b and the light is focusing by the optical couplingsystem to a focal point on a photodiode (not shown) of the RX 20 b. Thelight that is focused on the photodiode of the RX 20 b has about 70% to90%, and typically about 80%, of the optical power of the optical datasignal that passes out of the end 10 a of the MM optical fiber 10 andinto the optical coupling system 50. The other 10% to 30% of thereceived light, and typically about 20%, may pass into the laser diode(not shown) of the TX 20. This relatively small amount of light is notfocused on the laser diode, but is somewhat diffuse, and typically willnot significantly degrade the performance of the laser diode of the TX20.

The operations for the transmit and receive directions of the opticaltransceiver module 30 are identical to the operations described abovefor the transmit and receive directions of the optical transceivermodule 20. Therefore, in the interest of brevity, the operations of theoptical transceiver module 30 in the transmit and receive directionswill not be described herein. It should also be noted that although theoptical transceiver modules 20 and 30 shown in FIG. 1 are depicted aseach having a single TX channel and a single RX channel and associatedcomponents, the invention may be implemented in a parallel opticaltransceiver module that has a plurality of instances of the opticaltransceiver modules 20 and 30 and multiple respective optical fibers 10linking the respective modules together.

The stubs 90 a and 90 b are optional. If the stubs 90 a and 90 b are notused and no other techniques are used to eliminate interfacereflections, the link 1 may still operate satisfactorily, but there maybe a performance penalty in terms of increased signal degradation. Theinterface reflection is typically only approximately 4% of the totalenergy of the optical data signal. Therefore, it is possible to havesatisfactory performance without totally eliminating interfacereflection. Another option to using the stubs 90 a and 90 b is to employsome form of electronic equalization in the RXs 20 b and 30 b to cancelout the interface reflection. It is possible to use electronicequalization for this purpose due to the fact that any interfacereflection generally will always occur at the same instant in timerelative to the transmission of the optical data signal at the near-endoptical transceiver. For example, electronic equalizers (not shown) maybe used in the RXs 20 b and 30 b to perform interface reflectioncancellation. The manner in which electronic equalizers may be used toperform interface refection cancellation is known to persons of ordinaryskill in the art.

Assuming, for exemplary purposes only, that each of the TXs 20 a and 30a has a VCSEL or other laser diode that transmits at a data rate of atleast 10 Gb/s, and that each of the RXs 20 b and 30 b has a photodiode(e.g., a P-I-N photodiode) that is capable of detecting optical datasignals at a data rate of at least 10 Gb/s, then the aggregate data rateof the bi-directional optical link is at least 20 Gb/s. It should benoted, however, that the invention is not limited with respect to thedata rates of the TXs 20 and 30 or with respect to the aggregate datarate of the link 1.

FIG. 2 illustrates a side cross-sectional view of an exemplaryembodiment of the optical coupling system 50 functionally illustrated inFIG. 1. A laser diode (LD) 110 and a laser diode driver IC 111 of the TX20 a depicted in FIG. 1 are shown in FIG. 2. Also shown in FIG. 2 arethe photodiode (PD) 120 and the RX IC 121 of the RX 30 a depicted inFIG. 1. In accordance with this exemplary, or illustrative, embodiment,the optical beam splitter 50 a of the optical coupling system 50includes an integrated optical device comprising a substrate 50 b, aplurality of optical elements 50 c-50 e formed in or on the substrate 50b, an optical coupling structure 50 f disposed on an upper surface ofthe substrate 50 b, and a glass cover 50 g disposed on an upper surfaceof the optical coupling structure 50 f.

In addition to the optical beam splitter 50 a, the optical couplingsystem 50 includes a lens assembly 130. As will be described below 6-13,the lens assembly 130 is a part of an optical transceiver module (notshown). The lens assembly 130 mechanically couples the ends of aplurality of optical fibers 10 to the optical beam splitter 50 a,although only one of the optical fibers 10 can be seen in thecross-sectional side view of FIG. 2. Light being coupled between theoptical beam splitter 50 a and the ends of the optical fibers 10 passesthrough the glass cover 50 g. An array of refractive lenses 140 formedin the lens assembly 130 couple light between the ends of the opticalfibers 10 and the optical beam splitter 50 a. In the side view of FIG.2, only the components associated with only a single RX channel and asingle TX channel are shown. For example, only a single LD 110 of anarray of LDs and only a single PD 120 of an array of PDs are shown inFIG. 2. Correspondingly, only a single refractive lens 140 of an arrayof lenses and a single optical fiber 10 of an array of optical fibersare shown in FIG. 2.

The manner in which the optical beam splitter 50 a operates will now bedescribed with reference to FIG. 2. In the transmit direction, theoptical beam splitter 50 a operates as follows. A main light beam 141produced by the LD 110 is collimated by a “big eye” ball lens 112 andthe collimated beam is directed onto the optical element 50 c, which, inaccordance with this illustrative embodiment, is a diffractive opticalelement. The diffractive optical element 50 c may be configured toperform the collimation function, but using the big eye ball lenses 112for this purpose has certain advantages. In particular, using big eyeball lenses for this purpose allows manufacturing tolerances to berelaxed. In addition, using the big eye ball lenses 112 allows multiplesmall arrays of VCSELs instead of a single large array of VCSELs to beused for the LDs 110, which can provide significant cost savings.

The diffractive optical element 50 c splits the main light beam 141 intoa first light portion L1, a second light portion L2, and a third lightportion L3. The first light portion L1 has about 10% to 30%, andtypically about 20%, of the optical power of the main beam 141. Thefirst light portion L1 corresponds to the optical data signal that isultimately coupled into the end of the optical fiber 10 for transmissionover the link 1 (FIG. 1). The diffractive optical element 50 c alsoperforms a beam tilting operation that tilts the first light portion L1at a predetermined angle relative to an imaginary line (not shown) thatis normal to the substrate 50 b and that extends between the lower andupper surfaces of the substrate 50 b. In accordance with thisillustrative embodiment, the tilt angle ranges between about 5° and 10°,and is typically about 8°.

The tilted first light portion L1 passes out of the glass substrate 50 band into the optical coupling structure 50 f. The optical couplingstructure 50 f comprises a layer of replicated epoxy that operates onthe wavelength of light produced by the LD 110. The optical couplingstructure 50 f is shaped to include facets 50 f 1, 50 f 2 and 50 f 3that act as optically refractive and/or reflective elements. Facet 50 f1 operates as a refractive element that receives the tilted first lightportion L1 and tilts the beam such that the beam is normal to the uppersurface 50 g″ of the glass cover 50 g as the beam passes through theglass cover 50 g. In other words, the facet 50 f 1 reverses the degreeof tilt imparted on the first light portion L1 by the diffractiveoptical element 50 c. The glass cover 50 g, in accordance with thisillustrative embodiment, does not have any optical power, and therefore,has no optical effect on light passing through it. The purpose of theglass cover 50 g is to provide the optical beam splitter 50 a with aclear flat surface that enables it to be easily interfaced with the lensassembly 130, as will be described below in more detail with referenceto FIGS. 6-10

In the transmit direction, the refractive lens 140 of the lens assembly130 receives this light beam that passes through the glass cover 50 gand redirects it such that it is focused into the end of optical fiber10 for transmission over the link 1 (FIG. 1). As indicated above, thefirst light portion L1 that is coupled into the end of the optical fiber10 typically has only about 20% of the optical power of the main beam141. Reducing the optical power of the transmitted optical data signalin this manner ensures that the optical data signal is within eye safetylimits and yet has sufficient optical power to prevent signaldegradation from detrimentally affecting the performance of the link 1(FIG. 1). In addition, using the optical beam splitter 50 a to reducethe optical power of the transmitted optical data signal obviates theneed to use other methods and devices to attenuate the signal to a levelthat meets eye safety limits.

There are several advantages to using a relatively small tilt angle fortilting the first light portion L1 relative to the angle of incidence ofthe main beam on the diffractive optical element 50 c. An amount of tiltis needed to ensure that the optical beam splitter 50 a operatesproperly. For example, without some amount of tilt, light traveling inthe receive direction that is coupled from the ends of the opticalfibers 10 into the optical beam splitter 50 a might be directed into theaperture (not shown) of the LD 110 efficiently, which could potentiallydestabilize the laser operation. In addition, the relatively small tiltangle (e.g., 8°) allows the packaging of the optical beam splitter 50 ato be very compact and manufacturing tolerances to be relaxed. Largetilt angles can be optically and mechanically difficult to achieve.Splitters that provide large tilt angles sometimes encounterpolarization issues, and the materials that are used to make themsometimes have different properties at different angles. Most coatingsare designed for perpendicular applications and compensating for largerangles can be difficult. Also, coating thickness tolerances aregenerally tighter for larger angle designs than for smaller angledesigns. Thus, the relatively small tilt angle provided by thediffractive optical element 50 c obviates many of these manufacturingissues so that the optical beam splitter 50 a is easier to manufactureand can be manufactured to provide high optical precision andefficiency.

The second light portion L2 has about 70% to 90%, and typically about80%, of the optical power of the main beam 141. The second light portionL2 is the light portion that is ultimately absorbed by the beam stop 70a (FIG. 1). In the illustrative embodiment shown in FIG. 2, the secondlight portion L2 is reflected by the diffractive optical element 50 cinto a gap that exists between the LD 110 and the LD driver IC 111. Thelight that passes through this gap is incident on a top surface 151 of alead frame 150. The LD 110, the LD driver IC 111, the PD 120, and the RXIC 121 are secured to the upper surface 151 of the lead frame 150 by alayer of adhesive material 155, such as epoxy. In the embodiment of FIG.2, the light passes through the adhesive material 155 and is incident onthe upper surface 151 of the leadframe 150. The light is then reflectedby the upper surface 151 of the leadframe 150 onto the substrate of theLD driver IC 111 and is absorbed thereby. Thus, in accordance with thisillustrative embodiment, the substrate of the LD driver IC 111 functionsas the beam stop 70 a shown in FIG. 1. The light may be reflectedmultiple times between the upper surface 151 of the leadframe 150 andthe substrate of the laser driver IC 111 before the light is finallyabsorbed by the substrate.

The invention is not limited to using any particular device or materialas the beam stop 70 a. Essentially, any device or material thatfunctions as a light trap for light of the wavelength produced by the LD110 may be used for this purpose. For example, the adhesive material 155may be an epoxy that is absorptive to light of the wavelength that isproduced by the LD 110. As will be understood by persons skilled in theart, other types of light traps may be used for this purpose. Byabsorbing the second light portion L2 in this manner, the possibility ofstray light detrimentally impacting the operations of the opticaltransceiver module 20 (FIG. 1) is eliminated.

The optical coupling system 50 also splits off a small light portion L3of the main beam 141 for use in optical feedback monitoring. Inaccordance with this illustrative embodiment, the LD driver IC 111includes an array of monitor photodiodes 161, only one of which can beseen in the side cross-sectional view of FIG. 2, for monitoring theoptical output power levels of the LDs 110. The third light portion L3typically has about 1% to 2% of the optical power of the main beam 141,which is a sufficient amount for optical feedback monitoring. Thediffractive optical element 50 c tilts the third light portion L3 at arelatively small angle (e.g., about 15°) relative to an imaginary linethat is normal to lower surface of the substrate 50 b and that extendsbetween the lower and upper surfaces of the substrate 50 b. The facets50 f 2 and 50 f 3 act as a minor that internally reflects the thirdlight portion L3 to fold the third light portion L3 and direct it backdown through the substrate 50 b and onto the monitor photodiode 161.

In the receive direction, light L4 passing out of the end of the opticalfiber 10 is directed by the refractive lens 140 onto the facet 50 f 1.The facet 50 f 1 tilts the incoming beam by a predetermined tilt angleand directs it onto the diffractive optical element 50 c. Thepredetermined tilt angle is about 8° relative to an imaginary line thatis normal to the upper surface of the substrate 50 b and that extendsbetween the upper and lower surfaces of the substrate 50 b. Although asmall portion of the incoming beam L4 may pass through the diffractiveoptical element 50 c and fall on the LD 110, the tilt angle and thediffraction created by the diffractive optical element 50 c ensure thatthis small portion of light does not fall on the aperture of the LD 110,and therefore will not have a detrimental impact on the performance ofthe LD 110. Approximately 80% of the incoming light L4 that passes outof the end of the optical fiber 10 is directed by the diffractiveoptical element 50 c onto the optical element 50 d, which is areflective optical element. The reflective optical element 50 d is aminor that is created either by depositing a reflective layer of metalon the glass substrate 50 b to form a mirror or by depositing layers ofdielectric material on the glass substrate 50 b to form a dielectricminor.

The light that is incident on the reflective optical element 50 d isdirected by the reflective optical element 50 d onto a refractive lens50 e, which focuses the light onto the PD 120. Like the facets 50 f 1-50f 3 of the optical coupling structure 50 f, the refractive lens 50 e isformed of replicated epoxy, as will be described below in detail withreference to FIGS. 3A-5B. Although an array of the refractive lenses 50e are formed on the glass substrate 50 a, only one of the refractivelenses 50 e can be seen in the cross-sectional side view of FIG. 2.Alternatively, lens 50 e may also be a diffractive lens that focuses thelight onto the PD 120. This diffractive lens may also be formed ofreplicated epoxy.

The manner in which the optical beam splitter 50 a shown in FIG. 2 isfabricated will now be described with reference to FIGS. 3A-5B. FIGS. 3Aand 3B illustrate bottom and top perspective views, respectively, of aglass wafer 200 having arrays of the optical elements 50 c and 50 d,respectively, formed on the bottom and top surfaces 200 a and 200 b,respectively. With reference to FIG. 3A, the optical elements 50 ccorrespond to the diffractive optical elements 50 c described above withreference to FIG. 2. Although the wafer 200 is shown in FIG. 3A ashaving only about twenty of the diffractive optical elements 50 carrayed on the bottom surface 200 a thereof, there are typicallyhundreds or thousands of the diffractive optical elements 50 c formed onthe bottom surface 200 a of the wafer 200. The diffractive opticalelements 50 c have identical diffractive patterns formed therein. Thediffractive patterns may be formed in a variety of ways, such as byetching, chemical vapor deposition (CVD), sputtering, etc. Each of thediffractive patterns is essentially a holographic pattern made up of aseries of depth variations in the bottom surface 200 a, which can beformed by either removing portions in selected areas of the bottomsurface 200 a to create the depth variations or by adding material(e.g., metal) to selected areas of the bottom surface 200 a to createthe depth variations. For example, a wet or dry etching technique may beused to remove selected portions of the bottom surface 200 a, whereasCVD or sputtering may be used to selective add material to the bottomsurface 200 a of the wafer 200.

With reference to FIG. 3B, the optical elements 50 d correspond to therefractive optical elements 50 d shown in FIG. 2. The refractive opticalelements 50 d are minors formed either by depositing a reflectivecoating (e.g., metal) on the top surface 200 b or by depositing layersof a dielectric material on the top surface 200 b to create a dielectricmirror. Although the wafer 200 is shown in FIG. 3B as having only abouttwenty of the refractive optical elements 50 d arrayed on the topsurface 200 b of the wafer 200, there are typically hundreds orthousands of the refractive optical elements 50 d formed on the topsurface 200 b of the wafer 200.

FIGS. 4A and 4B illustrate the bottom and top surfaces 200 a and 200 bof the wafer 200 after an epoxy replication process has been used toform the refractive optical elements 50 e on the bottom surface 200 a ofthe wafer 200 and to form the optical coupling structure 50 f on the topsurface 200 b of the wafer 200. The epoxy replication process is a knownprocess that uses a master, or mold, to create a pattern, or replicathat is transferred to another surface. During the epoxy replicationprocess, a master having a shape corresponding to the shape of the arrayof optical elements 50 e is filled with a liquid epoxy. The epoxy isthen cured to transfer the shape of the master into the cured epoxy,thereby forming an epoxy replica 210. The master is separated from theepoxy replica 210, leaving the replica 210 disposed on the bottomsurface 200 a of the wafer 200 as shown in FIG. 4A. The epoxy replica210 covers the array of diffractive optical elements 50 c, but istransparent to the wavelength of light that is produced by the LD 110.Similarly, on the top surface 200 b of the wafer 200, the epoxyreplication process is performed during which a master having a shapecorresponding to the shape of the optical coupling structure 50 f isfilled with a liquid epoxy. The epoxy is then cured to transfer theshape of the master into the cured epoxy, thereby forming an epoxyreplica 220. The master is then separated from the replica 220, leavingthe replica 220 disposed on the top surface 200 b of the wafer 200 asshown in FIG. 4B.

FIGS. 5A and 5B illustrate bottom and top perspective views,respectively, of the optical beam splitter 50 a shown in FIG. 2. Afterthe epoxy replicas 210 and 220 have been created in the manner describedabove with reference to FIGS. 4A and 4B, a singulation process isperformed during which the wafer 200 is sawed to separate the opticalbeam splitters 50 a from one another. As indicated above, hundreds orthousands of the optical beam splitters 50 a may be formed on a singlewafer 200. Therefore, the manufacturing yield for the optical beamsplitter 50 a is very high and the splitters 50 a are manufactured withvery high precision. The optical beam splitter 60 a shown in FIG. 2 ismade by the same process and has a configuration that is identical tothe configuration of the optical beam splitter 50 a described above withreference to FIGS. 2-5A.

FIG. 6 illustrates a top perspective view of an optical transceivermodule 300 having an optical beam splitter holder 310 coupled therewiththat holds the optical beam splitter 50 a shown in FIG. 2. In FIG. 6,the only component of the optical beam splitter 50 a that is visible isthe glass cover 50 g. FIG. 7 illustrates a cross-sectional perspectiveview of the optical beam splitter holder shown in FIG. 6 with theoptical beam splitter 50 a held therein. With reference to FIG. 6, theoptical transceiver module 300 includes a printed circuit board (PCB)320, the leadframe 150 shown in FIG. 2 mounted on an upper surface ofthe PCB 320, and although not visible in FIG. 6, the LD 110, the LDdriver IC 111, the PD 120 and the RX IC 121 shown in FIG. 2 mounted onthe leadframe 150. The LD 110, the LD driver IC 111, the PD 120 and theRX IC 121 are blocked from view in FIG. 6 by the optical beam splitterholder 310. The PCB 320 has a land grid array (LGA) 330 formed on thelower surface thereof for electrically coupling the LD 110, the LDdriver IC 111, the PD 120, and the RX IC 121 to electrical contacts (notshown) of a motherboard (not shown) on which the optical transceivermodule 300 may be mounted.

Holes 340 a and 340 b formed in opposite ends of the optical beamsplitter holder 310 are shaped and sized to receive pins (not shown)located on the lens assembly 130 (FIG. 2), as will be described belowwith reference to FIG. 9B. Holes 350 a-350 d formed in the optical beamsplitter holder 310 are used to align the optical beam splitter holder310 with the optical transceiver module 300 when the optical beamsplitter holder 310 is being mounted on the optical transceiver module300. Retention features 360 a and 360 b formed on opposite ends of theoptical beam splitter holder 310 are used to mechanically couple theholder 310 to an optical connector (not shown), as will be describedbelow in more detail with reference to FIGS. 8-9B.

With reference to the cross-sectional perspective view of FIG. 7, themanner in which the optical beam splitter 50 a is held within theoptical beam splitter holder 310 is demonstrated. The lower surface 50g″ of the glass cover 50 g is mechanically coupled with the opticalcoupling structure 50 f of the optical beam splitter 50 a. The opticalbeam splitter holder 310 has an opening 370 a formed therein forreceiving and mating with the optical beam splitter 50 a. Portions ofthe lower surface 50 g″ of the glass cover 50 g rest on a recessed ledge370 b formed within the opening 370 a. The portions of the lower surface50 g″ of the glass cover 50 g that rest on the recessed ledge 370 b maybe secured to the recessed ledge 370 b by an adhesive material (notshown) to mechanically couple the optical beam splitter 50 a to theoptical beam splitter holder 310. The upper surface 50 g″ of the glasscover 50 g is flush with the upper surface 380 of the optical beamsplitter holder 310. These features eliminates gaps and enable the uppersurface 50 g″ of the glass cover 50 g to be easily cleaned by wiping theupper surface 50 g″ with a finger or a piece of cloth or other material.This is not a feature of optical transceiver modules that are currentlyavailable in the market. Most currently available optical transceivermodules have gaps in them that trap contaminates. Efforts to removethese contaminates are sometimes made by blowing air into the gaps, butoftentimes such efforts are unsuccessful. Of course, contaminatesexisting in the optical pathways can detrimentally affect theperformance of the optical transceiver modules. Thus, providing a beamsplitter configuration that enables the glass cover 50 g to be wipedclean to remove contaminates is highly advantageous.

FIG. 8 illustrates a perspective view of the optical transceiver module300 shown in FIG. 6 having an optical connector 400 coupled to it,which, in turn, has the lens assembly 130 shown in FIG. 2 coupled to it.FIGS. 9A and 9B illustrate top and bottom perspective views,respectively, of the optical connector 400 shown in FIG. 8 having thelens assembly 130 shown in FIG. 2 coupled to it. The lens assembly 130is mechanically coupled to the optical connector 400 by snap brackets410 a and 410 b formed on the optical connector 400 that snap intoindentations 130 a and 130 b, respectively, formed in the lens assembly130. The lens assembly 130 has pins 130 c and 130 d located thereon thatmate with the holes 340 a and 340 b (FIGS. 6 and 7), respectively,formed in the optical beam splitter holder 310. This mechanical couplingarrangement allows some freedom of movement of the lens assembly 130relative to the optical connector 400. In other words, the lens assembly130 “floats” relative to the optical connector 400, which ensuresprecision alignment of the lens assembly 130 with the optical beamsplitter holder 310 when the optical connector 400 is coupled with theholder 310, as will be described below in more detail.

The optical connector 400 has latches 420 a and 420 b formed on oppositeends thereof that mechanically couple with the retention features 360 aand 360 b, respectively, formed on the optical beam splitter holder 310.Although the optical connector 400 is typically made of a molded plasticmaterial that provides the connector 400 with a generally rigidstructure, the latches 420 a and 420 b flex to a limited degree whenengaged with the retention features 360 a and 360 b to provide a springforce that is exerted on the optical connector 400 to firmly pressportions 440 of the optical connector 400 against the optical beamsplitter holder 310. As the optical connector 400 and the optical beamsplitter holder 310 are pressed together in this manner and interlocked,the pins 130 c and 130 d formed on the lens assembly 130 mate with theholes 340 a and 340 b, respectively, formed in the optical beam splitterholder 310 to precisely align the lens assembly 130 with the opticalbeam splitter holder 310.

An optical fiber ribbon cable 450 comprising a plurality of opticalfibers 460 is coupled on an end thereof with the lens assembly 130 via acover 470 that presses the ends of the fibers 460 against V-shapedgrooves (not shown) formed in the lens assembly 130, as will bedescribed below in more detail with reference to FIG. 10. The refractivelenses 140 described above with reference to FIG. 2 are covered by apiece of protective tape 480 that protects the refractive lenses 140from contaminants.

FIG. 10 illustrates a cross-sectional side view of the opticaltransceiver module 300 shown in FIG. 8 coupled with the opticalconnector 400, which, in turn, is coupled with the lens assembly 130. InFIG. 10, the manner in which light is coupled between the ends of theoptical fibers 460 and the optical beam splitter 50 a is demonstrated.Like reference numerals in FIGS. 8-10 represent like components. Withreference to FIG. 10, the refractive lenses 140 formed on the lensassembly 130 are 45° minors. In the transmit direction, light producedby the LDs 110 is guided by the optical beam splitter 50 a in the mannerdescribed above with reference to FIG. 2 and is directed be the splitter50 a through the glass cover 50 g. The light directed through the glasscover 50 g is incident on the refractive lenses 140 and is reflected at45° angles onto the ends of respective optical fibers 460. In thereceive direction, light passing out of the ends of the optical fibers460 is incident on the refractive lenses 140 and is reflected at 45°angles such that the light is directed through the glass cover 50 g andis incident on the optical coupling structure 50 f. The received lightis then guided in the manner described above with reference to FIG. 2.

It should be noted that the invention has been described with referenceto a few illustrative, or exemplary, embodiments for the purposes ofdemonstrating the principles and concepts of the invention. It willunderstood by persons skilled in the art that the invention is notlimited to the embodiments described herein and that many modificationsmay be made to the embodiments described herein without deviating fromthe invention. For example, the invention is not limited to anyparticular configuration for the optical beam splitter 50 a or to anyparticular percentages for the optical power of the light portions thatare split off from the main beam. Also, which the optical beam splitter50 a has been described as having a bidirectional configuration forimplementation in a bidirectional link, the principles and conceptsdescribed herein are equally applicable to unidirectional applications.

1. An apparatus for mechanically coupling an optics system holder of anoptoelectronic module with an optical connector of the optoelectronicmodule, the apparatus comprising: first and second retention featuresformed on opposite ends of the optics system holder; and first andsecond latches formed on opposite ends of the optical connector, whereinwhen a lower surface of the optical connector is pressed against anupper surface of the optics system holder, the first and secondretention features engage the first and second latches, respectively,such that the first and second latches flex to a limited degree andexert a spring force on the optical connector that firmly presses thelower surface of the optical connector against the upper surface of theoptics system holder.
 2. The apparatus of claim 1, wherein the opticalconnector has one or more pins that protrude from the lower surface ofthe optical connector, and wherein the optics system holder has one ormore holes formed in the upper surface thereof, and wherein when thelower surface of the optical connector is pressed against the uppersurface of the optics system holder to cause the first and secondretention features to engage the first and second latches, respectively,respective pins of said one or more pins engage respective holes of saidone or more holes to align the optical connector with the optics systemholder.
 3. A method for mechanically coupling an optics system holder ofan optoelectronic module with an optical connector of the optoelectronicmodule, the method comprising: providing an optics system holder thatholds an optics system, the optics system holder having first and secondretention features formed on opposite ends; providing an opticalconnector having first and second latches formed on opposite endsthereof; pressing a lower surface of the optical connector against anupper surface of the optics system holder to cause the first and secondretention features to engage the first and second latches, respectively,wherein when the first and second retention features engage the firstand second latches, respectively, the first and second latches flex to alimited degree and exert a spring force on the optical connector thatfirmly presses the lower surface of the optical connector against theupper surface of the optics system holder.
 4. The method of claim 1,wherein the optical connector has one or more pins that protrude fromthe lower surface thereof, and wherein the optics system holder has oneor more holes formed in the upper surface thereof, and wherein when thelower surface of the optical connector is pressed against the uppersurface of the optics system holder to cause the first and secondretention features to engage the first and second latches, respectively,respective pins of said one or more pins engage respective holes of saidone or more holes to align the optical connector with the optics systemholder.